This invention relates to an aerodynamic drag-reducing shield for mounting on the front of a cargo-carrying compartment of a road vehicle. More particularly, the invention relates to a shield having a novel and advantageous surface contour.
The inventor is aware that there have been various prior proposals for devices for reducing the aerodynamic drag that is caused by the interaction of an air stream with the vertical flat front surface of the cargo-carrying compartment of a road vehicle in forward motion. Although many proposals for various forms of device have been made in the literature, few of these appear to have been reduced to a sufficiently practical form to render them commercially practicable propositions, and only a few devices are commercially available. Of the commercially available devices, most of these are devices intended to be mounted on the roof of the driver's cab of the vehicle. Generally, however, cab roof-mounted devices are efficient only when the wind direction is from directly ahead of the vehicle, and they are less efficient as sidewinds come into effect. Moreover, a roof-mounting is not always convenient as it may require that the roof should be strengthened to withstand the forces to which the air-deflecting devices are subjected, and the roof-mounting may interfere with other auxiliary devices that need to be mounted on the cab roof.
U.S. Pat. No. 4,021,069 in the name A.S. Hersh discloses an aerodynamic drag-reducing device which is mounted directly on the front surface of the cargo-carrying compartment of the vehicle. This device, which is generally of a paraboloid shape, significantly reduces the aerodynamic drag not only when in the case of a head-on air stream, but also a significant reduction in drag is obtained with air streams impinging at various angles from the side. The effects of drag reduction with sidewinds is of considerable importance, since as will be appreciated, the air stream that is incident on the road vehicle as a result of the combination of the effects of forward motion and of the actual atmospheric wind conditions is normally yawed with respect to the head-on direction, and analysis has shown that even at road speeds of up to 55 mph, the angle of yaw of the resultant air stream will normally exceed 5.degree. for at least about one-third of the time.
Although considerable savings in fuel consumption can be achieved by reducing aerodynamic drag, the efficiency of the device described in the above-mentioned Hersh U.S. Pat. No. 4,021,069 is not as great as may be desired.